Conventional computer entities have an operating system, applications, configuration data and user data stored for example on a direct or network attached storage device such as a hard disk drive component of the computer entity. Occasionally, catastrophic failure of a storage device may occur, in which case, an operating system, all applications, user data, and configuration of the computer entity are potentially lost.
It is known in the prior art to provide a ‘one button disaster recovery’ system, in which an operating system, applications, configuration data and user data are stored on a back up data storage device, for example a tape data storage medium, as a routine back up procedure. Under conditions of catastrophic failure of a hard disk data storage device of a computer entity, an operating system, applications, configuration settings and user data can be recovered from the external data storage medium, and loaded onto a new replacement hard disk data storage device. This known system is easy to use. Its activation generally requires a user to repair the hard disk data storage device of the computer entity, load the tape data storage medium containing the most recently recorded back up data into a drive unit, activate a single control button, and the computer entity automatically loads the operating system, applications, configuration settings and user data from the back up tape data storage medium, to reconfigure the new hard disk data storage device to a data state and configuration state which the computer entity held at the time of the last back up operation.
The prior art one button disaster recovery system based upon loading configuration data, applications and user data on a single data storage medium is very successful. However, for computer installations where unattended automated data recovery is required, it is known to store data on more than one individual data storage medium in a known data storage unit. These data storage units are known as ‘autoloaders’, or ‘libraries’. An autoloader/library may be used for unattended backup, where for example a different tape data storage cartridge is used each day with the selection of cartridges being under the control of the backup software. Several prior art data storage products are available which utilize a plurality of tape data storage cartridges in a single data storage unit. For example, a known high capacity back up solution may comprise a carousel of eight individual tape data storage cartridges in a single data storage unit.
Referring to FIG. 1 herein, there is illustrated schematically a prior art data storage unit capable of storing data to eight tape data storage cartridges, each having an uncompressed data storage capacity of 100 Gbytes. The data storage unit comprises a casing 100, having an entry port 101 for inserting and extracting tape data storage cartridges; a display and user interface 102, in a form of a liquid crystal display and a set of switches 103 for enabling a user to insert and extract tape data storage cartridges; a host interface bus, including a SCSI port or a fibre channel (FC) interface; a tape drive unit having read and write head, a tape transport mechanism, and a tape control mechanism for reading data from tape and writing data to tapes; an automatic loader device for loading individual tapes into and out of the tape drive unit; and a carrousel transport mechanism carrying a plurality of tape data storage cartridges within the casing, the loader unit capable of loading a tape data storage cartridge from the carrousel into the tape drive unit and vice versa.
Referring to FIG. 2 herein, there is shown schematically the data storage device of FIG. 1 in cut away view from above. A plurality of tape data storage devices 200-207 are carried on the carrousel 208 around the tape drive unit 209. A loader device 210 loads an individual tape data storage cassette 204 from the carrousel to the drive, and vice versa from the drive to the carrousel, under automatic control. Tape cartridges which are not in the tape drive unit, are stored on the carrousel within the casing.
With the prior art multi cartridge storage system, a plurality of tape data storage cartridges can be stored within a single data storage unit, thereby giving a high capacity data storage unit, and unattended data backup, typically using 1 tape data storage cartridge per day.
Using such data storage units, each day or more than once a day, a back up operation of a host computer will be performed. A different cartridge is used for each back up operation, and so typically there will be at least one tape data storage cartridge used for each day's back up. In some cases, back ups may be done twice per day, once in the morning and once in the afternoon. In other instances, back ups may be done at more regular intervals e.g. every hour.
The data storage unit shown in FIG. 1 is only one example of a prior art data storage unit, in this case, capable of containing eight known tape cartridges. However, much larger data storage units are available, containing more than 200 tape data storage cartridges. These devices are commonly known as ‘library’ units. In such library units, a plurality of tape cartridges are stacked in columns in a rack, and a robotic arm selects a tape cartridge from a physical column location, and delivers it into a tape drive unit for reading and writing, and once a read/write operation is performed, the robotic arm returns the tape cartridge back to its column location.
In a disaster recovery situation, where a hard disk drive unit of a computer entity is damaged beyond repair, using the prior art ‘one button disaster recovery’ system, after having replaced the damaged hard disk drive, or set of drives, the user selects the last back up tape cartridge to be created, inserts that back up tape cartridge into a tape drive unit associated with the computer entity, and reconfigures the new hard disk, and installation of data commences from the back up tape data storage cartridge. The tape drive unit is placed in a CD emulation mode, and the computer entity is power cycled, reading data from the tape data storage cartridge via the tape drive unit.
In a situation where a user is using more than one tape data storage cartridge for back up purposes and with a tape drive unit which only holds one tape cartridge at a time, the user must know which was the latest back up tape to be created. Since the operating system on the failed computer will not be up and running, there is no way of telling the last time or date on which the tape data storage cartridge was last written to, without the use of a different computer, or manually recording using an external means each time a backup is made. Typically, the user will have a pile of back up tapes, and unless the user has been careful to make good records, she will not know which tape to insert into the computers tape drive.
Where the computer entity is backed up to a data storage unit having multiple tape cartridges, there is a similar problem, that the user does not know which cartridge to select to initiate the disaster recovery. Selecting the wrong tape data storage cartridge causes recovery of the computer into a state which was not the most recent state before the disaster occurred.